The goal of the proposed research is to elucidate the mechanism by which antidiuretic hormone (ADH) promotes increased net water transport across the membranes of epithelial tissues. The specific aim is to determine the role in water transport of membrane delimited secretion granules in the affected cells. Study of fine structure, cytochemistry and physiology will be used to determine whether the hydroosomotic response and exocytosis and endocytosis can be separated or are obligatorially linked. Conditions known to promote or inhibit the hydroosmotic response or exocytosis will be tested for their effect on water transport and membrane flow. These will include: 1) in the whole animal, conditions of dehydration and stress; 2) in the isolated bladder, the application in vitro of colchicine and cytochalasin B; and 3) in isolated cells, the effect of Ca ions and ADH. Secretion granule and plasma membrane fractions separated by ultracentrifugation and free-flow electrophoresis from bladder epithelial cells will be analyzed in terms of their proteins, lipids and carbohydrates to elucidate the chemical basis for their permeability characteristics. The response of the secretion granule fraction to certain ions and osmotic conditions will be studied by electron microscopy in order to gain insight into the possible contributions of this organelle to the physiology of the bladder.